1. Field of the Invention
The present invention relates to an optical fiber amplifier for receiving pumping light and signal light, amplifying the signal light, and outputting thus amplified signal light; and an optical fiber for optical amplification employed in this optical fiber amplifier. In particular, the present invention relates to an optical fiber for optical amplifier in which at least a part of its core is doped with erbium, and an optical fiber amplifier using this optical fiber.
2. Related Background Art
As a technique for increasing the amount of transmittable information, i.e., channel capacity, in optical communications networks, wavelength division multiplexing (WDM) communications technology has been known.
In the WDM communications, there has been a demand for developing a super-wide band optical fiber amplifier which can simultaneously amplify WDM signal lights. An example of such a technology is disclosed in Makoto Yamada et al., "Super-wide Band Optical Fiber Technology Capable of Simultaneously Amplifying Communication Wavelength Band" (NTT Technical Journal, November issue, 1998, pp. 76-81). This publication discloses an optical amplifier in which an optical fiber amplifier section using an Er-doped optical fiber having an amplification region in the wavelength band of 1.55 .mu.m and an optical fiber amplifier section using an Er-doped optical fiber having an amplification region in the wavelength band of 1.58 .mu.m are connected in parallel, thereby yielding a wide flat gain region over both 1.55 .mu.m and 1.58 .mu.m bands.